In laser systems used for isotope separation, particularly uranium enrichment, an exemplary system being shown in U.S. Pat. No. 3,944,947, it is typical to provide a ring laser configuration for use as a laser pulse stretcher. By nature, such a configuration provides for recirculation of a portion of the laser radiation within the ring many times through an active lasing medium in order to achieve the stretching function. Because radiation is thus multiply recirculated throughout the system, any system perturbations, particularly those causing divergence or spreading of the beam, get amplified on each pass.
In applications of enrichment, the ultimately produced radiation beam at the output of a series of laser amplifiers placed subsequent to a ring laser is intended for use over many meters of beam distance to selectively ionize or excite vapor particles. The limitation of divergence, to as near a diffraction limited spreading as is possible, becomes a desirable if not necessary goal in such circumstances.
In the case of dye lasers used for the enrichment purpose a flowing dye solution is excited through an extended linear region transverse to the flow direction. The radiation generated or amplified is subject to degradation in beam quality, divergence for example, due to imhomogeneities in the dye solution. This divergence is prone to be greater in the direction of medium flow due to the fluid effects which contribute to the inhomogeneties.